1. Field of the Invention
The present invention relates to the procedure, practiced in the course of the commercial manufacture of a book, known as "backing" the book block and, particularly, to the processing of a previously rounded book block to shape the spine region thereof so as to place it in condition to receive a cover. More specifically, this invention is directed to apparatus for imparting the requisite shape to the spine of a book block in order to prepare the book block for the application of a cover thereto and, especially, to apparatus which forms a pair of creases in the opposite sides of a clamped, previously rounded book block adjacent to the spine thereof. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
In the production of a book, prior to the application of a cover thereto, it is known to sequentially round and back the stack of ordered sheets which define the book block. The backing operation is conventionally performed with the use of a shaped part that is caused to move backwards and forwards over the entire breadth of the book block spine. As a result of the friction and application of pressure which accompanies these movements, the edge regions of the sheets comprising the book block are folded away from the center of the book block spine, i.e., the sheets comprising the book block are bent outwardly generally in the direction of the two opposite sides of the block. The angles through which the printed sheets are folded increase in the outward direction from the book block center. The net result is the imparting of a stable, mushroom-like shaped spine region to the book block.
An example of a prior art book rounding and backing machine of the type generally discussed above is disclosed in published German Application 1,536,507.
The curvature of the traditional rounded shape of the spine region of a book block will vary from book-to-book, i.e., there are a multiplicity of radii of curvature which must be accommodated by a book manufacturer. In order to reliably achieve the requisite shape, there must be a matching of the book contacting member(s) of the backing apparatus, i.e., the pressing beam(s), to the desired spine radius. However, bearing in mind that there are a multiplicity of radii, this matching is feasible only within narrow limits. Restated, taking into account the economic and physical constraints which limit the number of parts which may held in inventory, and further taking into account the relatively long set-up time of the prior art backing machines, the choice of pressing beam shape has in the past always been a compromise. When there is a comparatively gross mismatch between the shape of the pressing beam and the spine radius, there is an inherent risk of degradation of the quality of the product. This is particularly true in the case of book blocks comprised of sheets having a low flexural stiffness and/or in the situation where the book block to be subjected to the backing operation has not been backlined, i.e., a book block which simply has had an adhesive applied in the spine region and which thus exhibits a high coefficient of friction. The degradation results from the fact that, as the pressing beam executes its return movement to the center of the book block, the printed sheets, which have been bent over towards the sides of the block during the working stroke, will be dragged back with the tool. Such bending followed by a dragging back can lead to the "collapse" of the creased sheets.